CN111175670A - Ground fault inversion implementation method of distribution automation test system - Google Patents
Ground fault inversion implementation method of distribution automation test system Download PDFInfo
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- CN111175670A CN111175670A CN201910695014.2A CN201910695014A CN111175670A CN 111175670 A CN111175670 A CN 111175670A CN 201910695014 A CN201910695014 A CN 201910695014A CN 111175670 A CN111175670 A CN 111175670A
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- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
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Abstract
The invention discloses a method for realizing earth fault inversion of a distribution automation test system, which comprises the steps of reading an earth fault simulation waveform file; converting the sampling frequency in the waveform file into a proper sampling frequency through an interpolation algorithm; scaling the sampling values of the corresponding channels; acquiring sampling points from the first cycle of the initial steady state of the waveform file, and calculating by using an FFT (fast Fourier transform) algorithm to obtain the amplitude of the initial steady state of the waveform and the compensation steady state before the fault point of the initial phase angle structure fault waveform; acquiring a sampling point from the last cycle of the last stable state of the waveform file, and calculating by using an FFT (fast Fourier transform) algorithm to obtain the amplitude and the initial phase angle of the last stable state of the waveform file, namely the compensation stable state after the fault point is constructed; the system combines a ground fault inversion state sequence according to the compensation steady state before the fault, the compensation steady state after the fault and the ground fault waveform after the sampling frequency conversion; the technical problems of low testing efficiency, poor flexibility and the like are solved.
Description
Technical Field
The invention belongs to the field of distribution network automation, and particularly relates to a method for realizing ground fault inversion of a distribution automation test system.
Background
With the improvement of the requirement on the reliability level of the power distribution network and the rapid development of power distribution automation, in order to rapidly troubleshoot the ground fault, the distribution line fault indicator is widely applied to the power distribution network, and whether the line ground fault can be rapidly and correctly identified is a main important factor influencing the reliable operation of the power distribution network. Therefore, each large electric power company uses the ground fault recognition function of the fault indicator as an important test index for the network access detection of the equipment.
At present, two neutral point grounding modes, namely a large current grounding mode and a small current grounding mode, are generally used for the power distribution network in China. The former includes direct neutral grounding, grounding via low (medium) resistance and low (medium) reactance, etc.; the latter includes grounding of the neutral point, through an arc suppression coil, or through a high resistance.
When a large-current grounding fault occurs, the three-phase voltage is not balanced any more, and the fault is generally removed in time by line protection, so that serious consequences are prevented. After a low-current grounding fault occurs, the three-phase voltage still keeps balance, the fault current is small, the line overload can not be caused generally, and the protection action of the line can not be triggered. The operation can be continued for 2h after the low-current ground fault. However, if the fault point is not detected in time for processing, the insulation of the equipment is accelerated to age due to the reduction of the grounding phase voltage and the increase of the non-fault phase voltage, so that the insulation damage is caused, even the insulation breakdown is possibly caused, the iron core of the voltage transformer is saturated, the exciting current is increased, and the voltage transformer is burnt out after long-time operation. After the grounding fault occurs, intermittent arc grounding may occur to cause resonance overvoltage, which is several times or even several times of the normal voltage, and the overvoltage will greatly endanger the insulation of the power transformation equipment, so that the insulation breakdown of the power transformation equipment causes more accidents.
The distribution line fault indicator testing system generally outputs a simulated ground fault waveform through inversion to test the ground fault identification function of the distribution line fault indicator. Before the simulated ground fault point occurs, the test system needs to output a steady-state alternating current of several seconds to tens of seconds to ensure that the test sample can normally work and identify the ground fault. Aiming at the requirement, most of the current test systems realize the steady-state and simulation ground faults before the faults occur by inverting waveforms. Therefore, the data volume of the waveform file can be greatly increased, the time for the test system to issue the waveform data to the power source module is increased, and the test efficiency is reduced. Meanwhile, if the test parameters are changed, the waveform file of the whole state needs to be generated through re-simulation, and the flexibility is poor.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method is used for solving the problems that most of the existing test systems completely realize stable state before fault occurrence and simulated ground faults by inverting waveforms, so that the data volume of waveform files can be greatly increased, the time for the test systems to issue waveform data to a power source module is increased, and the test efficiency is reduced; meanwhile, if the test parameters are changed, the waveform file of the whole state needs to be generated through simulation again, and the flexibility is poor.
The technical scheme of the invention is as follows:
a method for realizing earth fault inversion of a distribution automation test system comprises the following steps:
step 1: opening a waveform file of the ground fault analog waveform to be issued, and reading sampling frequency, total number of sampling points N and sampling value y of each analog channelkK is 0,1,2, …, N-1, channel unit, channel gain coefficient and channel offset coefficient;
step 2, converting the sampling frequency in the waveform file into an integer multiple frequency of 3200HZ through an interpolation algorithm, wherein N belongs to N to obtain a ground fault waveform after the sampling frequency conversion, so as to calculate a front and rear steady state characteristic value of the waveform by using an FFT (fast Fourier transform) algorithm subsequently;
step 3, scaling the sampling values of the corresponding channels according to the waveform voltage and current transformation ratio parameters;
step 4, acquiring sampling points from the first cycle of the initial steady state of the waveform file, calculating by using an FFT (fast Fourier transform) algorithm to obtain the amplitude and the initial phase angle of the initial steady state of the waveform, and constructing a compensation steady state before a fault waveform fault point;
step 5, acquiring sampling points from the last cycle of the last stable state of the waveform file, calculating by using an FFT (fast Fourier transform) algorithm to obtain the amplitude and the initial phase angle of the last stable state of the waveform, and constructing a compensation stable state after a waveform fault point;
and 6, combining the ground fault inversion state sequence by the distribution automatic test system according to the compensation steady state before the fault, the compensation steady state after the fault and the ground fault waveform after the sampling frequency conversion.
It still includes:
and 7, the distribution automatic test system issues the ground fault inversion state sequence data to the power source, controls the power source to output the ground fault inversion state sequence, and performs ground fault related tests on the tested sample.
The interpolation algorithm in step 2 is realized by the following steps: converting the sampling frequency in the COMTRADE waveform file into an integer multiple frequency of 3200HZ 64 x 50HZ, namely 3200nHZ, and N belongs to N by using a piecewise linear interpolation algorithm; the piecewise linear interpolation algorithm formula is as follows:
in the formula: x is the number ofiFor a given interpolation node, also a sampling time point in the waveform file, yiFor sampling a time point xiThe corresponding value of the sampled value is,
is xiAnd xi+1The estimation interpolation corresponding to any time point x; calculating to obtain a sampling time interval [ x ] according to the formulai,xi+1]Interpolation of any point in time.
Step 3, when the sampling values of the corresponding channels are scaled according to the waveform voltage and the current transformation ratio parameters, the waveform voltage and the current transformation ratio parameters are changeable; the scaled sample values are:
and (4) the scaled sampling value is (the sampling value after interpolation is processed is channel gain coefficient + channel offset coefficient) variable ratio parameter.
Step 4, the method for acquiring the sampling point from the initial steady first cycle of the waveform file comprises the following steps: the sampling frequency is 3200nHZ, N is equal to N, the number of sampling points contained in a single cycle is 64N, 64 sampling points are uniformly sampled from the first steady cycle of the waveform file, and the sampling points are represented as s1k＝ykn,k＝(0,1,2,...,63)。
Step 5. last week of unstability of the slave waveform fileThe method for acquiring sampling points in the wave comprises the following steps: the 64 sampling points are uniformly sampled from the last steady cycle of the waveform file, and if the total number of sampling points of the waveform file is N, the sampling points can be represented as s2k＝yN-(63-k)n-1,k＝(0,1,2,...,63)。
The invention has the beneficial effects that:
the prior art carries out ground fault related test on a sample, and generally needs to apply steady state alternating current of several seconds or tens of seconds to the sample before a fault occurrence point. If all the simulation is carried out by the fault waveform, the fault simulation waveform needs to be generated repeatedly, the data volume of the waveform file can be greatly increased, the requirement on the storage capacity of hardware is improved, the time required by waveform issuing is increased, and the testing efficiency is reduced. The invention only needs to issue the fault waveform of a certain time before and after the fault occurrence point, and the rest is realized by the compensation steady state sequence obtained by calculation, thereby obviously improving the test efficiency and simplifying the test flow.
The front and back compensation steady-state duration and the current and voltage transformation ratio of the fault waveform can be set as required, so that the steady-state duration is increased or reduced, the amplitude of the fault waveform is amplified or reduced, and the use flexibility of the fault waveform file is improved.
The compensation steady state is calculated by using an FFT algorithm, so that the compensation steady state can be smoothly connected with the analog waveform.
The invention carries out interpolation processing on the analog waveform file, changes the sampling frequency, can properly reduce the waveform data amount and improve the waveform data issuing efficiency.
The method solves the problems that the existing test system completely realizes the steady state before the fault and the grounding fault of simulation by inverting the waveform, so that the data volume of the waveform file can be greatly increased, the time for the test system to send the waveform data to the power source module is increased, and the test efficiency is reduced; meanwhile, if the test parameters are changed, the waveform file of the whole state needs to be generated through re-simulation, and the technical problems of poor flexibility and the like are solved.
Drawings
FIG. 1 is a ground fault inversion state sequence;
FIG. 2 is a schematic flow chart of the present invention;
FIG. 3 illustrates a ground fault simulation waveform in accordance with an exemplary embodiment;
FIG. 4 is a ground fault inversion state sequence of a test system output in an embodiment.
Detailed Description
A method for realizing earth fault inversion of a distribution automation test system comprises reading fault waveform file data, performing interpolation processing, and converting sampling frequency of a waveform file; scaling the waveform data according to the set waveform transformation ratio parameter; respectively obtaining initial steady-state data of a cycle wave and sampling data of a cycle wave steady state at the tail of a waveform file, and respectively obtaining the amplitudes and initial phase angles of the initial steady state and the final steady state of the fault waveform through an FFT (fast Fourier transform) algorithm; synthesizing a ground fault inversion state sequence, as shown in fig. 1, wherein the duration of the compensation steady state before and after a fault can be set according to the test requirement; the distribution automation test system outputs the state sequence to test the tested device.
The flow of the implementation method is shown in fig. 2, and the specific steps are as follows:
step 1: and opening a COMTRADE waveform file of the ground fault analog waveform to be issued, and reading data in the COMTRADE waveform file, wherein the COMTRADE waveform file comprises the sampling frequency, the total number N of sampling points, a sampling value yk (k is 0,1,2, …, N-1), a channel unit, a channel gain coefficient, a channel offset coefficient and other information of each analog channel.
Step 2: converting the sampling frequency in the COMTRADE waveform file into a proper sampling frequency through an interpolation algorithm to obtain a ground fault waveform after the sampling frequency conversion; the method is convenient for calculating the steady-state characteristic values before and after the waveform by using the FFT algorithm.
Taking the use of piecewise linear interpolation algorithm and 64-point FTT fast Fourier transform algorithm as an example: the sampling frequency in the COMTRADE waveform file is converted to an integer multiple of 3200HZ, i.e., 3200nHZ, N ∈ N, using a piecewise linear interpolation algorithm. The piecewise linear interpolation algorithm formula is as follows:
wherein x isiFor a given interpolation node, also a sampling time point in the waveform file, yiFor sampling a time point xiThe corresponding value of the sampled value is,
is xiAnd xi+1Any time point x between the estimated interpolation. According to the formula, the sampling time interval [ x ] can be calculatedi,xi+1]Interpolation of arbitrary time points.
And step 3: the variable-ratio parameters of waveform voltage and current which can be set are provided. And scaling the sampling value of the corresponding channel according to the set value. The processed sample values are represented by the following formula:
to-be-issued sampling value
(processed sampling value after interpolation channel gain coefficient + channel offset coefficient) variable ratio parameter
And 4, step 4: sampling points are obtained from the first cycle of the initial steady state of the waveform file, the amplitude and the initial phase angle of the initial steady state of the waveform are calculated through an FFT algorithm, and a compensation steady state before a fault waveform fault point is constructed. The steady state output duration can be freely set as desired.
Taking the waveform file data processed in the steps 2 and 3 as an example: the sampling frequency is 3200nHZ, N ∈ N, and the number of sampling points contained in a single cycle is 64 ×.n. The 64 sampling points are uniformly sampled from the first steady cycle of the waveform file, and can be expressed as
And the method is used for calculation of FTT fast Fourier transform algorithm.
And 5: and acquiring a sampling point from the last cycle of the last stable state of the waveform file, calculating by using an FFT (fast Fourier transform) algorithm to obtain the amplitude and the initial phase angle of the last stable state of the waveform, and constructing a compensation stable state after the waveform fault point. Also, the steady-state output duration can be freely set as needed.
Taking the waveform file data processed in the steps 2 and 3 as an example: the 64 sampling points are uniformly sampled from the last steady cycle of the waveform file, and if the total number of sampling points of the waveform file is N, the sampling points can be represented as s2k＝yN-(63-k)n-1And k is (0,1, 2.., 63) and is used for calculation of an FTT fast Fourier transform algorithm.
Step 6: and the distribution automation test system combines the calculated pre-fault compensation steady state, post-fault compensation steady state and the ground fault waveform after sampling frequency conversion into a ground fault reverse state sequence.
Fig. 3 shows a ground fault simulation waveform, which has 6 channels, and includes the currents Ia, Ib, Ic, and the voltages Ua, Ub, Uc in sequence. As can be seen, there are about 5 steady state cycles before a fault occurs and about 11 steady state cycles after a fault occurs.
FIG. 4 is a ground fault inversion state sequence of the test system output. Compared with the graph shown in fig. 3, the compensation steady states before and after the fault, which are calculated by the FFT algorithm, can be smoothly connected with the ground fault simulation waveform.
And 7: the distribution automation test system sends the ground fault inversion state sequence data to the power source, controls the power source to output the ground fault inversion state sequence, and conducts ground fault correlation test on the tested sample.
Claims (6)
1. A method for realizing earth fault inversion of a distribution automation test system comprises the following steps:
step 1: opening a waveform file of the ground fault analog waveform to be issued, and reading sampling frequency, total number of sampling points N and sampling value y of each analog channelkK is 0,1,2, …, N-1, channel unit, channel gain coefficient and channel offset coefficient;
step 2, converting the sampling frequency in the waveform file into an integral multiple frequency of 3200HZ through an interpolation algorithm, wherein N belongs to N to obtain a ground fault waveform after the sampling frequency conversion, so as to calculate a front and rear steady state characteristic value of the waveform by using an FFT algorithm subsequently;
step 3, scaling the sampling values of the corresponding channels according to the waveform voltage and current transformation ratio parameters;
step 4, acquiring sampling points from the first cycle of the initial steady state of the waveform file, calculating by using an FFT (fast Fourier transform) algorithm to obtain the amplitude and the initial phase angle of the initial steady state of the waveform, and constructing a compensation steady state before a fault waveform fault point;
step 5, acquiring sampling points from the last cycle of the last stable state of the waveform file, calculating by using an FFT (fast Fourier transform) algorithm to obtain the amplitude and the initial phase angle of the last stable state of the waveform, and constructing a compensation stable state after a waveform fault point;
and 6, combining the ground fault inversion state sequence by the distribution automatic test system according to the compensation steady state before the fault, the compensation steady state after the fault and the ground fault waveform after the sampling frequency conversion.
2. The method of claim 1, further comprising:
and 7, the distribution automatic test system issues the ground fault inversion state sequence data to the power source, controls the power source to output the ground fault inversion state sequence, and performs ground fault related tests on the tested sample.
3. The method for implementing ground fault inversion of the distribution automation test system according to claim 1, characterized in that: the interpolation algorithm in step 2 is realized by the following steps: converting the sampling frequency in the COMTRADE waveform file into an integer multiple frequency of 3200HZ 64 x 50HZ, namely 3200nHZ, and N is equal to N by using a piecewise linear interpolation algorithm; the piecewise linear interpolation algorithm formula is as follows:
in the formula: x is the number ofiFor a given interpolation node, also a sampling time point in the waveform file, yiFor sampling a time point xiThe corresponding value of the sampled value is,
is xiAnd xi+1The estimation interpolation corresponding to any time point x; calculating to obtain a sampling time interval [ x ] according to the formulai,xi+1]Interpolation of arbitrary time points.
4. The method for implementing ground fault inversion of the distribution automation test system according to claim 1, characterized in that: step 3, when the sampling values of the corresponding channels are scaled according to the waveform voltage and the current transformation ratio parameters, the waveform voltage and the current transformation ratio parameters are changeable; the scaled sample values are:
and (4) the scaled sampling value is (the sampling value after interpolation is processed is channel gain coefficient + channel offset coefficient) variable ratio parameter.
5. The method for implementing ground fault inversion of the distribution automation test system according to claim 1, characterized in that: step 4, the method for acquiring the sampling point from the initial steady first cycle of the waveform file comprises the following steps: the sampling frequency is 3200nHZ, N is equal to N, the number of sampling points contained in a single cycle is 64N, 64 sampling points are uniformly sampled from the first steady cycle of the waveform file, and the sampling points are represented as s1k＝ykn,k＝(0,1,2,...,63)。
6. The method for implementing ground fault inversion of the distribution automation test system according to claim 1, characterized in that: step 5, the method for acquiring the sampling point from the last cycle of the last steady state of the waveform file comprises the following steps: the 64 sampling points are uniformly sampled from the last steady cycle of the waveform file, and if the total number of sampling points of the waveform file is N, the sampling points can be represented as s2k＝yN-(63-k)n-1,k＝(0,1,2,...,63)。
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